1. Field of the Invention
This invention relates to medical apparatus. More particularly, this invention relates to mechanisms for applying pressure to a leg of the human body in conjunction with the treatment of venous ulcers of the leg and possibly with other forms of medical treatment (e.g., sclerotherapy or vein stripping/removal for treatment for varicose veins) of the leg or other extremity.
2. State of the Art
A venous ulcer is damage and loss of skin above the ankle that is the result of a problem with the veins in the leg. Venous ulcers typically develop on either side of the lower leg, above the ankle and below the calf. They are difficult to heal and often recur.
The veins of the leg are divided into the superficial and deep systems according to their position relative to the fascia.
The deep veins, which come together to form the popliteal and femoral veins lie within the fascia and are responsible for the venous return from the leg muscles. Dilated valve less sinusoids also lie within the fascia (more particularly in the soleus and gastrocnemius muscles). The sinusoids fill with blood when the leg is at rest.
The long saphenous vein which runs along the medial side of the leg from foot to groin and the short saphenous vein which runs at the back of the calf from foot to knee are the major vessels of the superficial venous system. These vessels lie outside the fascia and are responsible for the venous return from the skin and subcutaneous fat.
Communicating veins, sometimes called perforators because they perforate the deep fascia, join the two systems. The perforators, like the other veins in the leg, contain valves that permit the flow of blood in one direction only, from the outer or superficial system inwards to the deep veins.
The venous pressure at the ankle of a subject who is lying supine is around 10 mmHg, but on standing this will rise considerably due to an increase in hydrostatic pressure (equivalent to the weight of a vertical column of blood stretching from the point of measurement to the right auricle of the heart).
During walking, as the foot is dorsally flexed, the contraction of the calf muscle compresses the deep veins and soleal sinuses thereby emptying them of blood. As the foot is plantarly flexed, the pressure in the veins falls, the proximal valves close, and the veins are refilled by blood passing through the perforators from the superficial system. During this cycle, in a normal leg, the distal valves of the deep veins and the valves of the perforators will ensure that the expelled blood can go in only one direction—upwards, back to the heart.
Blockage or damage to the venous system will cause disruption to normal blood flow, which may manifest itself in a number of different ways according to the site and extent of the damage. If the valves in the superficial system are affected, venous return will be impaired and blood may accumulate in the veins causing them to become distended, leading to the formation of varicosities (varicose veins).
If the function of the perforator valves is impaired, the action of the calf muscle pump will tend to cause blood to flow in the reverse direction into the superficial system increasing the possibility of damage to the superficial vessels.
Following a deep vein thrombosis that results in complete or partial obstruction of a deep vein, the unrelieved pressure produced by the calf muscle pump on the perforator valves may cause these to become incompetent. In this occurs, there will be a large rise in the pressure in the superficial system, which may force proteins and red cells out of the capillaries and into the surrounding tissue. Here, the red cells break down releasing a red pigment that causes staining of the skin, an early indicator of possible ulcer formation.
Venous leg ulcers are generally shallow and red in color. The skin surrounding the ulcer is frequently discolored due to the staining described previously. Incompetent perforating vein valves can also cause malleolar venules to become dilated and appear as fine red threads around the ankle. This condition, called ankle flair, is also diagnostic of a venous ulcer.
For patients with venous disease, the application of external compression can help to minimize or reverse the skin and vascular changes described previously, by forcing fluid from the interstitial spaces back into the vascular and lymphatic compartments. As the pressure within the veins of a standing subject is largely hydrostatic, it follows that the level of external pressure that is necessary to counteract this effect will reduce progressively up the leg, as the hydrostatic head is effectively reduced. For this reason it is usual to ensure that external compression is applied in a graduated fashion, with the highest pressure at the ankle. The preferred value for the degree of pressure varies according to a number of factors, including the severity of the condition and the height and limb size of the patient.
Medical hosiery represents a useful and convenient method of applying compression to normal shaped legs in order to prevent the development or recurrence of leg ulcers. However, these stockings are of limited value in the treatment of active ulceration, being difficult to apply over dressings. In such situations compression bandages currently represent the treatment of choice. Compression bandages apply a pressure to the limb that is directly proportional to bandage tension but inversely proportional to the radius of curvature of the limb to which it is applied. This means, therefore, that a bandage applied with constant tension to a limb of normal proportions will automatically produce graduated compression with the highest pressure at the ankle. This pressure will gradually reduce up the leg as the circumference increases.
As can be readily appreciated, it is cumbersome and difficult to apply uniform tension to the compression bandage as it is applied to the treated limb, and thus this is accomplished only by highly skilled caregivers. Moreover, once secured to the treated limb, care and attention must be given to ensure that the bandage does not slip or become displaced as this will lead to multiple layers forming, which in turn may lead to localized areas of high pressure, which can place the patient in direct risk of skin necrosis.
Mechanical compression treatments have also been proposed. An exemplary compression device is described in U.S. Pat. No. 5,031,604 to Dye. As generally described at col. 2, lines 33 et seq., an arrangement of chambers are provided that circumscribe the leg. An active pneumatic control system controls the pressure in the chambers to squeeze the leg near the ankle and then squeeze sequentially upward toward the knee in order to move blood from the extremity toward the heart. As noted in col. 4, lines 20-59 of U.S. Pat. No. 6,488,643 to Tumey et al., the mechanically produced compression levels may produce ischaemic (i.e., localized tissue anemia) not noted at similar compression levels obtained through bandaging. It may also produce cuffing (i.e., a reduction in leg pulsatile blood flow). The pneumatic control system is also bulky and heavy, which severely limits the mobility of the patient during treatment. Moreover, the pneumatic control system fails to provide a mechanism to ensure that excessive pressure, which can cause necrosis, is not applied to the treated limb. These limitations have resulted in most mechanical compression devices being contraindicated for patients exhibiting deep-vein thrombosis. Consequently, those skilled in the art have to date avoided such mechanical compression devices for the treatment of venous ulcers or edema of the extremities.
Thus, there are many problems, obstacles and challenges associated with the current treatments of leg ulcers and there is a need in the art to provide an apparatus for the treatment of venous ulcers (or an adema or other wound of the leg) that is simple to use, that is sure to produce the desired treatment, and that does not severely limit the mobility of the patient.